The present invention relates to apparatus for making helical wire coils from metallic, plastic or other wire. More particularly, the invention relates to improvements in apparatus for making wire coils of the type which can be subdivided into spiral binders for threading into the perforations of steno pads, exercise books and analogous stationary products.
Apparatus of the above outlined type comprise a rotary coiling mandrel and several pin-shaped wire guiding elements which are disposed around the periphery of the mandrel to form a helical path whose inlet receives a continuous length of wire from a suitable feeding device. The distribution of guiding elements at the periphery of the mandrel corresponds to the desired lead or pitch of the wire coil. The purpose of the guiding elements is to guide the wire as well as to cause successively formed convolutions of the coil to advance axially of the mandrel.
An apparatus of the just outlined character is disclosed, for example, in German Pat. No. 1,902,623. The guiding elements are cylindrical pins which are non-rotatably mounted at the periphery of the mandrel and form several rows. Thus, the wire which is in the process of being converted into the convolutions of a coil must slide along the peripheral surfaces of stationary pins. Those end portions of the pins which are adjacent to the mandrel have a concave shape conforming to the convex shape of the peripheral surface of the mandrel. This renders it possible to use the pins into immediate proximity of the mandrel, i.e., the clearances between the concave end faces of the pins and the mandrel are narrower than the diameter of the thinnest wire which is to be converted into a coil. Therefore, even a very thin wire is not likely to penetrate between the mandrel and one or more pins where it could jam and necessitate a lengthy interruption of operation of the winding apparatus. Each interruption is especially undesirable when the apparatus is installed in a complete production line which converts larger sheets into a succession of stationery products wherein stacks of overlapping sheets are held together by spiral binders.
Since the pins of the patented apparatus are cylindrical bodies and the wire has a round cross section, the wire is in mere point contact with the pins and slides therealong, i.e., the slippage between each pin and the wire is 100 percent. Such point contact between the wire and the pins results in highly localized and highly pronounced stressing of the wire, i.e., the wire is subjected to pronounced compressive and deforming stresses which are likely to result in damage to the surface of the wire, especially if the wire comprises a metallic core and a plastic sheath around the core.
Another apparatus is disclosed in German Offenlegungsshrift No. 2,234,633 which proposes to use guiding elements in the form of ball bearings. The wire contacts and thereby rotates the outer races of the ball bearings. Such apparatus can be used only for the making of large-diameter wire coils, i.e., for the processing of relatively thick wire, because (when compared with the diameters of pin-shaped guiding elements) the diameters of the ball bearings are rather large and such bearings occupy a substantial amount of space at the periphery of the mandrel so that they cannot be used for the making of coils having a small pitch, i.e., with convolutions closely adjacent to each other. Therefore, when the wire coil is to be made of thin wire, the apparatus which is disclosed in the aforediscussed German Pat. No. 1,902,623 is preferred over the apparatus which employs guiding elements in the form of ball bearings. In other words, when a conventional apparatus is to produce small-diameter wire coils of thin wire and small pitch, at least some damage to the surface of the wire is unavoidable. Alternatively, such relatively small wire coils cannot be made of certain types of wire, namely, of wire having a plastic sheath which is likely to be damaged on contact with fixedly mounted stationary cylindrical guiding elements.